This invention relates generally to a composition where the occurrence of opacity or clarity is regulated to occur to selected temperatures, and a method to make such a composition. It is the purpose of this invention to develop and use new compositions for temperature indication between -150.degree. C. and +250.degree. C. In addition the invention aims to create a composition which will indicate when either over- or under-exposure to a related temperature range has occurred. Such a reaction occurs in a reversible way in order that one may take corrective action.
Recommended storage temperatures for food, medicines, biological products, etc. are always related to conditions ideal for safeguarding the stability of the products. Such products should be stored in such a way that the initial quality may be satisfactorily preserved until they are used or consumed. Some products are to be neither frozen nor warmed up above a certain temperature during the storage period. For instance, a number of vaccines are recommended to be stored between +2.degree. C. and +8.degree. C. These preparations, in addition, should not be frozen. Packages of dairy products and meat products are stored in the refrigerator at temperatures with a recommendation that such products should not be exposed to temperatures higher than, for example, +8.degree. C. Even if there would be no direct danger to the quality of the products when stored wrongly for a short time, it is obvious that prolonged storage or handling under unfavourable temperature conditions would naturally harm or deteriorate the products quality. It is, therefore, of importance to have an instrument which can easily indicate such wrong handling in order that one may take corrective action so as to avoid quality deterioration. Other fields of application lie in other temperature regions, for instance, green, fruits, flowers etc.--products all of which are sensitive to freezing. It is the aim of the invention to adjust to a product's ideal storage temperature range and by an easily observable way to show if the product is correctly stored.